Eli Lilly and Co. will spend $140 million to construct an 88,000-square-foot plant southwest of downtown Indianapolis to make cartridges for insulin pens.

The Indianapolis-based drugmaker announced details of the expansion Thursday morning at a press conference on the site of the new plant on South Harding Street. The new plant, first announced on Tuesday, will adjoin Lilly’s existing manufacturing complex, known as the Lilly Technology Center.

About 100 workers will staff the new plant, which will be constructed by spring 2014 and ready for operations in 2015. But only “some” of that number will be additional jobs on top of the 3,000 manufacturing workers Lilly already employs in Indianapolis, according to Lilly.

Wages for the new jobs will be similar to those earned by Lilly's existing manufacturing work force, although Lilly officials declined to disclose details.

Lilly officials also said they plan to apply for tax abatements from the city.

“This expansion reinforces our commitment to manufacturing here in Indianapolis,” said Maria Crowe, Lilly’s president of manufacturing operations. Lilly’s last manufacturing expansion in Indianapolis was more than 20 years ago.

Crowe said Lilly needs the new plant because demand for insulin continues to rise in the United States and globally. The company already makes insulin cartridges in Italy and France, and will continue to expand those plants, too.